1. Field of the Invention
The present invention relates to the manufacture of microelectronic devices. An improved method places dopant on and within a dielectric or semiconductor surface. More particularly, the invention pertains to a process of diffusing and activating p-type and n-type dopants in dielectric or semiconductor substrates by means of electron beam irradiation.
2. Description of the Prior Art
This invention relates to electron beam system and method and more particularly to a system and method for optimizing the placement of dopant material on a dielectric or semiconductor surface area. Ion implantation is a semiconductor doping process whereby a plurality of dopant atoms are first ionized, and then accelerated to velocities sufficient to penetrate the semiconductor surface and deposited therein. It is well known to produce semiconductors whose electrical behavior can be altered by the introduction of minute quantities of elemental materials called “dopants.” Dopants are either p-type or n-type. P-type dopants produce what is commonly known as hole conductivity while n-type dopants produce what is commonly known as electron conductivity. Combinations of hole and electron-rich regions produce the desired devices such as transistors, resistors, diodes, capacitors, etc., which form the basis of microelectronic device operation. Recent advances in semiconductor manufacture include fine-line geometries of dopant materials placed on a substrate to form very large scale integrated devices. Integrated circuits are generally formed by connecting the numerous individual devices made by dopant implantation. A single wafer may contain several thousand devices which are individually packaged as a single monolithic circuit. It is important that the doping process be accurately done in order to ensure the circuit operates according to design parameters. If doping does not bring about such operation, then the corresponding yields may be drastically reduced thereby adding to the cost of manufacture. Important factors relating to accurate doping are the need to control the number of doping ions introduced in the surface material, the need to control the uniformity of doping ions placed across the surface, the need to control the depth or concentration profile of dopant placed into the surface, and the need to ensure the doping pattern can be introduced as a maskable pattern on the surface. Each of these factors must be closely monitored and can be achieved by several different techniques.
In the fabrication of complimentary metal-oxide-semiconductor (CMOS) circuits, dopants can be introduced by several different methods, including ion implant processing, spin-on dopant diffusion and bulk diffusion of dopant into non-masked surface regions. Another technique may involve direct sourcing of an ion beam at select fine-line areas into non-masked regions. The latter technique generally involves ion beam implantation system. Ion implant processing has become the method of choice for advanced devices. Once the dopant is introduced into the semiconductor substrate it must be distributed properly and activated to provide the proper/desired electrical properties in the semiconductor. The conventional method of achieving the diffusion and activation of dopants is thermal processing. This has been done by furnace processing or rapid thermal annealing. The furnace process is usually a long process of heating at a high temperature, for example 30 minutes to 6 hours at 600° C. to 1700° C. There are several problems with thermal processing to achieve diffusion and activation of dopants. The random thermal motion of the dopant atoms in the semiconductor lattice does not necessarily achieve the desired distribution of the dopant atoms in the device. Thermal activation of the dopant is a random process and therefore it is difficult to accurately control the activation of the dopant to achieve the desired electrical properties. The high temperatures involved in diffusion and activation of dopants can be detrimental to the overall performance of the device as each time the substrate is heated, all dopants in the substrate can continue to diffuse. Thus, it would be desirable to use low temperatures and short processing times.
According to this invention an electron beam is applied to the substrate, in conjunction with heating the substrate, to achieve the diffusion and activation of the dopant in the substrate. This addresses the problems involved in thermal processing. By using an electron flux at a given energy the depth of the electrons can be controlled very accurately. Thus the dopant atom motion can be limited to the region where the electrons interact with the substrate, and not necessarily the random thermal motion throughout the entire substrate as in thermal processing. By using an electron flux at a given energy and dose, the activation of the dopant can be very precisely controlled to achieve the desired electrical properties in the substrate. By relying on the kinetic energy to carry out the diffusion and activation of the dopants the peak temperature of the process can be reduced, thus improving uniformity.